HIV cellular targets: Which host immune cells are most frequently infected and depleted during HIV disease progression?

Introduction / Context: HIV pathology centers on progressive loss of cellular immunity. The virus primarily targets cells expressing CD4 and appropriate chemokine co-receptors (CCR5/CXCR4), leading to immunodeficiency and susceptibility to opportunistic infections.

Given Data / Assumptions:

• Main target marker: CD4 surface glycoprotein.
• Co-receptors: CCR5 early, CXCR4 later in some strains.
• We are asked to name the most affected lymphocyte subset.

Concept / Approach: CD4+ T helper lymphocytes orchestrate immune responses. HIV entry requires gp120 binding to CD4, then to a co-receptor, followed by fusion via gp41. Loss of CD4+ T cells correlates with disease staging and defines AIDS at critical thresholds (e.g., CD4 < 200 cells/µL or AIDS-defining illness).

Step-by-Step Solution: Identify receptor usage: CD4 as primary receptor. Connect receptor to cell type: CD4+ T lymphocytes. Select the option naming this subset explicitly.

Verification / Alternative check: Laboratory monitoring of HIV relies heavily on CD4 counts and percentages; ART recovery is tracked by CD4 reconstitution.

Why Other Options Are Wrong: CD8+ T cells are crucial for control but are not the principal infected/depleted subset; “Null cells” is nonspecific; “None” and “mast cells only” are incorrect.

Common Pitfalls: Confusing activation-induced CD8+ expansion with primary HIV tropism; overlooking macrophages and dendritic cells as additional targets but not the main defining subset for staging.

Final Answer: CD4+ T lymphocytes.